Elementary energy bands concept, band structure, and peculiarities of bonding in β-InSe crystal

Abstract

The elementary energy bands concept together with the analysis of the Davydov-like splitting were applied for the first time for investigation of energy band structure and spatial electron density distribution in hexagonal crystals. This approach was used for consideration of the valence band states and for determination of peculiarities of the spatial charge density distribution in the unit cell of the layered b-InSe crystal. It was established that the valence charge density can be located in the so-called Van-der-Waals space. Conclusions following from the elementary energy bands concept were confirmed by the ab initio calculations of the band structure of b-InSe.

Non‐standard anisotropy of the energy spectrum of a layered TlGaSe2 crystal

“…This ratio for the electron and hole effective mass obtained in the parabolic approximation for the directions ${\Gamma} {-} Q_{1} $ and ${\Gamma} {-} F_{1} $ is abnormal, since one should expect that $(m_{e,h}^{*} /m_{0} )_{{\Gamma} {-} N} $ should be larger than $(m_{e,h}^{*} /m_{0} )_{{\Gamma} {-} Q_{1} ,{\Gamma} {-} F_{1} } $ . A similar situation took place in the case of other indium and gallium selenides 2, 12, 13, 26. The abnormal dispersion in the direction $Q_{1} {-} {\Gamma} {-} F_{1} $ is caused in our opinion, also by a low‐energy non‐parabolicity of the dispersion relation $E({\bf k})$ for the conduction band.…”

“…Thus, the application of the empty‐lattice approximation allowed to predict the symmetry of states creating the EEBs that constitute the valence band of TlGaSe 2 . As we demonstrated 10–13, there is a relation between the obtained in this way EEBs and the so‐called actual Wyckoff position in the unit cell, where the maximum of the spatial valence electron density distribution is focussed. By analysing its coordinates and checking if they represent, e.g.…”

“…The recent ab initio band structure calculations 5 were performed within the Brillouin zone that does not correspond to that of monoclinic base‐centered lattice. In the present paper we verify the band structure calculations of TlGaSe 2 , perform the analysis of its symmetry, topology, and the existence of the Davydov splitting using the concept of the elementary energy bands (EEBs) 6–13. We analyse additionally a possibility of existence of abnormal dispersion of electronic spectrum branches and related to it the effective mass of charge carriers that takes place in the case of other complicated layered crystals (e.g.…”

“…The concept of the EEBs developed by us in recent years, see e.g. 10–13, allows to predict in a quick way the symmetry and topology of the energy spectrum and the spatial valence electron density distribution in a unit cell based upon the empty‐lattice approximation. Hence, we establish in the beginning the symmetry of states of TlGaSe 2 energy spectrum obtained in the empty‐lattice approximation for the Γ point.…”

Engineering a topological phase transition in β-InSe via strain

“…Indium selenide (InSe) and other III-VI layered semiconductors have received extensive attention due to the unusual nature of the electronic interaction and also because of their applications in solar energy conversion, nonlinear optics, terahertz generation and memory devices [26][27][28][29][30][31]. At a more fundamental level, the band structure of InSe presents some specific features that are related to the strong anisotropy of its electronic structure [28].…”